"Kipling Williams, a Purdue University psychologist, studied how people felt when a young woman walked by them and either made eye contact, made eye contact while smiling..."

"... or completely ignored them. Even brief eye contact increased people's sense of inclusion and belonging. 'Just that brief acknowledgment, that brief glance — with or without a smile — made them at least temporarily feel more socially connected,' Williams says. And it works both ways. Those that had been 'looked through' felt even more disconnected than the control group. So, how can we dodge the risks of loneliness and stop short-changing our own happiness? It might be easier than you think. 'It takes very little to acknowledge somebody's existence,' Williams says."

From "Want To Feel Happier Today? Try Talking To A Stranger" (NPR).

So people feel happier if a young woman smiles and/or makes eye contact. Does that suggest that all of us can make each other happier by making eye contact and smiling? More research is needed.

But I do like the idea of finding a way to acknowledge the existence of strangers — not every stranger along the way, but various people you encounter. We tend to put a lot of energy into the people who have an ongoing role in our life — family, friends, co-workers — but I think completely transitory relationships with random strangers are important. I think there's beauty and idealism in sharing something for a moment with absolutely no expectation of getting anything more.